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River hydraulics – a view from midstreamDonald W. Knight aa School of Civil Engineering, The University of Birmingham, Birmingham, UK E-mail:Version of record first published: 08 Feb 2013.

To cite this article: Donald W. Knight (2013): River hydraulics – a view from midstream, Journal of Hydraulic Research,51:1, 2-18

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Journal of Hydraulic Research Vol. 51, No. 1 (2013), pp. 2–18http://dx.doi.org/10.1080/00221686.2012.749431© 2013 International Association for Hydro-Environment Engineering and Research

Vision paper

River hydraulics – a view from midstreamDONALD W. KNIGHT (IAHR Member), Emeritus Professor Water Engineering, School of Civil Engineering, The University ofBirmingham, Birmingham, UKEmail: d.w.knight@bham.ac.uk

ABSTRACTSix distinct “views” of river hydraulics are presented, beginning with what influences us today, given our shared history, to what we can learn fromothers as they tackled research topics in their day. Other views relate to how we regard rivers through laboratory studies, the computer screen or innature at full scale, and to how we might view research problems in the future. Interspersed with these various views are 10 questions that are frequentlyasked of river engineers, along with some possible answers. In attempting to answer these particular questions, some insights gained from a career inriver hydraulics research are offered as a guide to others, both in practice or academe, as they raise some further issues which are worth reflecting on.This paper is particularly aimed at emerging hydraulic researchers and young engineers who are embarking on a career in river hydrodynamics.

Keywords: Flood modelling; history of hydraulics; hydraulic education; hydraulic resistance; laboratory studies; open-channel flowturbulence; river channels

1 Introduction

We are all standing midstream in the river of knowledge, asColeman (2010) helpfully reminds us of in his review of flu-vial morphology. Like water in a river, the knowledge we relyon flows from the past to the present, where our task is to addsomething useful to it today, before it flows on to future genera-tions, who will interpret it and develop it yet further. Just as it isgood sometimes to pause by a river, simply to enjoy it and takein the view, so it is appropriate for us to pause occasionally inour intellectual endeavours, to take stock of where our disciplinehas come from and to reflect on where it might be going to in thefuture. This paper is particularly aimed at emerging hydraulicresearchers and young engineers who are embarking on a careerin river hydrodynamics.

Some “vision” papers try to second guess developments,while others attempt to review the key elements of current under-standing and only then to elucidate tentatively what might be.Two such comprehensive and insightful reviews worth readingare those titled: “Issues and Directions in Hydraulics” by Nakatoand Ettema (1996) and “Perspectives in Fluid Dynamics” byBatchelor et al. (2003).

As part of the Hydraulics Colloquium in honour of ProfessorJohn F Kennedy, held at the Iowa Institute of Hydraulic Research

in 1996, I had the privilege and task of attempting to sum up theissues raised concerning river mechanics. In doing this, I also pre-sented 25 quotations from various reviews on hydraulic researchover several decades. They are worth reading and passing on tostudents because, like epigrams and epitaphs, they encapsulatewisdom or insight in a few words. Here are just five:

(1) “Why has progress in river engineering been so slow? Firstrecall that most river sedimentation research is carried outby geologists and engineers. By the very nature of its sub-ject, geology is not predisposed to dramatic developments(although its parent subject, geophysics, is); and engineersare made inherently conservative by the consequences ofmistakes in their subject. So it is, I believe, that sedimentengineering has proceeded step by step, with successive gen-erations happy to set their shoes in the larger footprints madeby the handful of intellectual adventurers, enumerated above,who went before them; and content if they merely madeslightly deeper imprint in the sand” (Kennedy 1989).

(2) “I strongly suspect, however, that early creative bursts ofinsight seldom occur when one is staring at equations, orexperimental data, or computer printout. Instead, novel ideasseem to me to arrive at unexpected times, when one isworking on a problem but not momentarily immersed in it.

Revision received 10 November 2012/Open for discussion until 31 August 2013.

ISSN 0022-1686 print/ISSN 1814-2079 onlinehttp://www.tandfonline.com

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In my experience, new ideas most often come while I amhiking, gardening, fishing, showering, or engaged in someother seemingly unscientific pursuit” (Kennedy 1989).

(3) “The broadening of knowledge, like the introduction of newtools like numerical methods, results in specialisation ofthe profession which then implies a loss of general viewof hydraulic problems. One consequence of specialisation isthe widening of a gap between fluids research and the prac-tice of hydraulic engineering. Closure of this discontinuitywill require the efforts of both camps in a variety of ways.Research oriented professionals should devote more time towriting books and monographs that sort, collate, evaluate andtranslate into usable terms the relevant research results. Prac-tising engineers should share their real-world experiencesincluding technical failures with universities. This exchangehas to become part of continuous education” (IAHR 1993).

(4) “Finally, the mathematical model referred to in the paper isbased on the solution of Newton’s second law of motion(developed in 1687), using the Taylor-Maclaurin infiniteseries (developed in 1715) and including the Darcy frictionfactor (developed in 1889) and Prandtl’s turbulence theory(developed in 1925). Many of these equations and exper-imental observations had little relevance at the time. Themathematical model outlined herein has been applied to over50 environmental impact assessment projects, both in the UKand overseas. It is therefore of fundamental importance that,within the profession, the value of basic original researchmust never be forgotten” (Falconer 1990).

(5) “Turbulent motions contribute significantly to the transportof momentum, heat and mass in most flows of practicalinterest and therefore have a determining influence on thedistributions of velocity, temperature and species concen-tration over the flow field. It is the basic task of engineersworking in the field of fluid mechanics to determine these dis-tributions for a certain problem, and if the task is to be solvedby a calculation method, there is no way around makingassumptions about the turbulent transport processes. Basi-cally this is what turbulence modelling is about: becausethe turbulent processes cannot be calculated with an exactmethod, they must be approximated by a turbulence modelwhich, with the aid of empirical information, allow the tur-bulent transport quantities to be related to the mean flowfield” (Rodi 1980).

For the remaining quotations, together with details of thenumerous issues raised concerning possible future directions forriver engineering, see Nakato and Ettema (1996) and Knight(1996). There are, of course, many other books dealing withthe fundamentals or specific aspects of flow in open channels,that contain excellent reviews of current knowledge, such as“Floodplain Processes” (Anderson et al. 1996), “Coherent FlowStructures in Open Channels” (Ashworth et al. 1996), “Mixingand Transport in the Environment” (Beven et al. 1994), “Tur-bulence in Open-Channel Flow” (Nezu and Nakagawa 1993),

“Turbulence Models and their Application in Hydraulics” (Rodi1980), to name but a few. Several IAHR reports (IAHR 1993,1994, 1999) also embody research visions as do some spe-cific journal papers (Kennedy 1983, 1987, 1989, Elder 1986).Although it is clearly beyond the scope of this paper to give acomprehensive list of references, a selection of papers has beenmade, some to reflect the variety of subject matter, some forhistorical perspective, and some for whetting the appetite of thereader or to illustrate a particular point in the text.

2 A view of the upstream boundary conditions

Following the theme of a river of knowledge, it is obvious that theupstream flow and boundary conditions affect us, conditioningour understanding of river mechanics and in some cases pollut-ing it. For example, our own understanding today may becomeclearer by some ground-breaking piece of mathematical analy-sis, or alternatively possibly muddied by poor experimental dataand incorrectly drawn conclusions. A good understanding of theliterature is therefore essential, not only for the academic, butalso for the practicing engineer, who may use software based onadvanced theoretical concepts. Two of the common weaknesses Ihave encountered over my career in candidates for PhD examina-tions are: (1) their lack of appreciation concerning the historicaldevelopment of certain fundamental concepts in fluid mechanicsand (2) their reluctance to read any papers more than 25 years old,that is, before they were born. Undergraduates likewise are oftennot taught about the philosophical development of ideas in fluidmechanics, which is especially remiss, given a subject aboundingin fascinating history, personalities and conflicting opinions. See,for example, the exchange of letters between Osborne Reynoldsand Sir Gabriel Stokes, given by Allen (1970) in the book aboutOsborne Reynolds by McDowell and Jackson (1970), concerningthe relative importance/superiority of mathematics over exper-imental coefficients in engineering (or vice-versa), which is astopical today as it ever was over 100 years ago. Froude’s earlyretirement at the age of 36 and his tenacity in building a 76 m longtowing tank near his home to test the use of scale model shipsis also instructive. His subsequent arguments with senior navaland government “experts” in the Admiralty show that it is notalways easy to explain new developments to those who are unre-ceptive to new ideas. But who now thinks it unusual to use scalemodels to determine the optimum hull shapes or wave resistancefor boats, as evidenced by tests on military ships or yachts forthe America Cup race? Stories about people will always amuseundergraduates, as will anecdotes. Classical fluid mechanics andhydrodynamics is a rich seam with which to entertain and intereststudents of any age. As well as teaching the history of the devel-opment of hydraulic concepts (Rouse and Ince 1957, Rouse 1976,1978, 1980, Hager 2003, 2009, Viollet, 2007), students shouldbe introduced to the philosophy of science as part of a sound edu-cation as well as how scientific ideas interact with the politicalprocess.

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One example that illustrates the usefulness of backgroundreading for students is that related to the well-known Colebrook–White equation. Although Professor White’s output in publishedwork was minimal (only 20 papers in 40 years), his researchactivities were wide-ranging, influential and long lasting. Hisresearch was based on fundamental theoretical ideas, good con-ceptual thinking, backed up by detailed experimental work, allundertaken with exquisite attention to detail, followed up by theformulation of the results into a dimensionally correct equationafter suitable validation studies had been undertaken. In thatera, basic knowledge of fluid flow behaviour concerning bound-ary layers and turbulence may not have been as extensive as itis today, but researchers then were well grounded in the fun-damentals of fluid flow behaviour, theoretical approaches andassumptions. They also knew well the history of their subjectand previous key works. White well knew that the Nikuradseroughness length is only one parameter to consider when dealingwith roughness, as highlighted further by Morvan et al. (2008)in recent times. His earlier experimental work, as indicated byDavies and White (1929), Pendennis-Wallis and White (1939),Colebrook and White (1937), pursued many details of secondaryflows, curvature and types of roughness, all adding value to thefinal paper written by his associate (Colebrook 1939) in which thewell-known formula appears. If only young undergraduate andpostgraduate students of today took as much care about the histor-ical context of their work, especially its philosophy and implicitassumptions, and took as much care over their experimentalwork, just as Professor White did, then we might have moreproductive research output today. Other examples that might becited are the early works of Hele-Shaw (1899, Hele-Shaw andHay 1900), which contain such exquisite detail and photographsthat would be exceedingly hard to improve on today. The reason-ing behind the development of well-known equations is anotherincentive to read original works, rather than a later second-hand“explanation” of them. I wonder how many students have everconsulted the original paper by Chezy in 1768 or looked up whatManning actually wrote in 1889, let alone read Yen (1991)?

Different types of publication should also be appreciated.Short papers, often proposing a new idea, are particularly usefulas they indicate the first fresh description of a phenomenon thatmay be of lasting value. The paper by Einstein and Li (1958),describing secondary currents in straight channels is one suchexample of a brief informative nugget, whereas the later muchlonger paper by Perkins (1970) is invaluable reading as a fol-low up. Academic papers such as Grass et al. (1991), which atfirst sight might not seem to have much relevance or impact onpractical issues, should likewise not be ignored, as also ground-breaking work by many PhD students, for example, Tehrani(1992), to name one among many that could be mentioned. Pic-ture books of fluid flow are also extremely useful, as illustrated bythe one on “Visualized Flow” by the Japan Society of Mechan-ical Engineers (JSME 1988). As always, knowledge acquisitionis a time consuming task, but thankfully now much simpler withtools like Google Scholar than it used to be. A regular habit of

reading the contents pages of journals, or occasionally browsingthrough the stack rooms of libraries still yields surprising gems,often in a serendipitous moment, and helps to protect againstthe dangers of the specialization/broad understanding problemraised in the third quotation of the introduction.

3 A view from the river banks

It is often said that river engineering is an “art” as well as a“science”, and that modelling should therefore take into accounttwo distinct elements: “theoretical fluid mechanics” and a mul-titude of “practical issues”. This is illustrated by Fig. 1, takenfrom Nakato and Ettema (1996), in which river engineering isenvisaged as the joining together of two river banks, one named“theoretical fluid mechanics” and the other “practical problems”.On the left hand side (looking downstream), the shapes of thezones represent various practical river problems and their inter-related nature. The idea for this came to me after seeing thesketch by Lighthill (1966) in which the various types of wavesin liquids and gases were displayed in a similar manner, with theshapes and positions, reflecting particular wave characteristicsand possible interactions with their neighbouring phenomenon.

To deal with a specific practical issue in river engineering,one has to understand its relationship with other problems, gainthat knowledge, cross the river by one of the bridges, pick upthe appropriate theoretical knowledge from the right hand bank(again looking downstream), return by another bridge and dealwith the particular practical problem or issue in question. In doingso, one may have to repeat the journey several times, or recol-lect previous journeys, thus slowly building up a more completepicture of the river system itself. The two river banks should nottherefore be regarded as opposites, but as complementary. Some-times a false dichotomy develops between people who tend toinhabit one side of the river or the other, perhaps stereotyped bythe outdated “division” between practitioners and theoreticians,each regarding the other side as being either “too academic”, “toosimple” or maybe a worse epithet. However, rivers always havetwo banks, and the most fruitful advances in river engineeringhave often occurred when the two sides meet, exchange viewsand deal with common issues.

It should be noted that the various areas of theoreticalknowledge also have regions too. The river bank alongside thecontinuity and Navier–Stokes equations has sheet piling, indicat-ing that the bank is firm and well established. It has been theresince 1845. However, the sheet piling barely extends into the tur-bulence region, where the ground appears to be marshy and notso well developed. The high rise buildings nearby indicate enor-mous growth, activity and development in this region, as typifiedby the growth in the subject of computational fluid dynamics andadvanced experimental studies in turbulence. A deeper under-standing of turbulence is, however, for future generations toachieve.

Although it is said that a sketch is worth a thousand words,visual images can create lasting impacts, so it is important to

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Figure 1 The art and science of river engineering (after Knight) (reproduced from Nakato and Ettema (1996), page 448)

recognize that a poor drawing of a fluid flow phenomenon cansolidify ones thinking into believing that it is a true represen-tation of reality. An example of this, drawn from the author’sexperience, is described later. Likewise, a common danger ininterpreting model output is to believe that the visualizations(e.g. vector plots, velocity fields, etc.) are a true representationof the physical process. What is seen can be an artefact of thevisualization algorithms and not a true reflection of the solution ofthe numerical procedures in the hydrodynamic simulation. Forexample, post-processing of raw outputs may have smoothedresults or introduced false flow structures. There is sometimes atendency for users to give greater weight to more detailed pic-torial output from a two-dimensional (2D) or three-dimensional(3D) model, than from a one-dimensional (1D) model or mea-surements. Having now mentioned models, it is appropriate toconsider briefly the impact of computer modelling.

4 A view from the computer screen

Mathematical models that deal with whole catchments, com-bining hydrological models with hydraulic models of flows in

individual rivers, have changed fundamentally the way riverengineering is now practiced compared to say 50 years ago.Flood risk management, eco-hydrodynamic and geomorphicstudies have all been transformed by the development of pow-erful numerical tools and techniques that solve the governingequations. The process of obtaining the most significant con-cepts, through model building to achieve particular objectives,calibration and commercial exploitation is complex, as any-one knows who has attempted it. It is possibly worthy of areview in its own right. Some experiences of this process aredescribed in Abbot and Basco (1989), Abbot et al. (1991),ASCE (1988), Cunge et al. (1980), Knight et al. (2010a), Knight(2008, 2013), Mc Gahey et al. (2008) and Nakato and Ettema(1996).

In dealing with complex technical issues, and particularlywhen trying to explain an issue to government officials or politi-cians, it is a good practice to pose the issue in the form of a simplequestion with the key technical issues highlighted immediatelyafterwards. This undoubtedly helps them to understand unfamil-iar material and, hopefully, to go on to appreciate the relevanceof the scientific issues raised. This approach is now used here andin subsequent sections to illustrate several important hydraulic

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issues that arise in river engineering. In all, some 10 questionsare posed.

Question 1 – What level of modelling is generally required inriver engineering?

Key issue: appropriate model selection and correctapplication

• There is generally a range of models available. It is essentialthat the user is able to select the best model for each applica-tion and is aware of the shortcomings and uncertainties of thechosen method.

• Correct model selection and application will pay for itselfmany times over in terms of improved accuracy and certaintyin the results.

The river engineer has to select the right tool, for example, theappropriate 1D, 2D and 3D model, for any particular job, and thisdemands considerably more knowledge and understanding thanwas required in the past. Today, the questions that are likely to beasked are: When should one adopt a 2D depth-averaged numeri-cal model to represent the flow physics, rather than a 1D model?When one uses a 3D model, what type should it be and whatlevel of turbulence closure is appropriate? The experience of themodeller in using 2D and 3D models is now also important, as dif-ferent answers will be obtained by different users, not only due tosubtle differences in model type and calibration requirements butalso according to what type and version of commercial softwareis used. Some background is provided in Abbott et al. (1991), inprevious reviews (ASCE 1988) and in IAHR guidelines (IAHR1994).

Depth-averaged models are commonly used in practice. How-ever, depth-averaging of velocities in rivers, especially in sinuousand meandering channels, may lead to false representation ofactual flow patterns. For example, where the velocity vectorsvary over the depth, depth-averaging in a preferred directionwill give misleading results, especially so when used to calcu-late the discharge. This is commonly seen in flood conditions atthe cross-over region of a meandering channel, where the upperflow from the floodplain interacts with the flow below the bank-full level in the main channel. The former is predominately inthe valley slope direction whereas the latter is predominately inthe channel streamwise direction. Thus, in some circumstances,a 3D model might be preferable, and so one has to ask at whatstage should a 3D model be considered? The use of hybrid mod-els, such as a 1D river model with a 2D floodplain model, alsoraises a number of technical issues.

It is worth noting at this point that higher dimensionalityof a model does not necessarily lead to better accuracy in theresults. In certain cases, the opposite may be true. The principle ofOccam’s razor should always be applied – that of starting with thesimplest by assuming the least (Pluralitas non est ponenda sinenecessitate; “Plurality should not be posited without necessity”,William Occam, 1285–1347). The principle gives precedence to

simplicity; of two competing theories, the simplest explanationof an entity is to be preferred. In the context of modelling flows inrivers, this suggests caution before embarking on 3D modellingfor solving every type of river engineering problem. It should beremembered that very often simple tools are still used to craftworks of art and beauty. Just consider what can be done with apaintbrush, chisel and tape measure. It is the skill to which theyare put that portrays the “usefulness” of the tools.

As regarding accuracy and certainty, at least three pointsshould be kept in mind, discretization, averaging and equifinality.Morvan et al. (2008) write that

Roughness appears in fluid mechanics as a consideration at wallboundaries, to account for momentum and energy dissipation thatare not explicitly accounted for in the simplified or discrete for-mulae used in numerical engineering and science. In this wayroughness is a model of the physical processes that are omitted.There is indeed no need for such an artefact in the continuummechanics Navier–Stokes (NS) equations for laminar flow, orin the Reynolds Averaged Navier–Stokes (RANS) equations forturbulent flow, since all momentum and other energy losses –such as turbulence, shear, drag force, etc. – are implicitly con-tained in the equations. The issue only arises when the exactform of the equations needs to be simplified, as for example indiscretisation purposes in three-dimensional (3-D) models, andfor discretisation and conceptual reasons in 2-D and 1-D models.In the latter, the definition of the so-called ‘roughness’ or ‘fric-tion factor’ becomes more uncertain, and therefore less rigorousin terms of definition and sizing, than it does for 3-D models,although it must be said that it does not account for the samething as in 3-D models.

Then, Nikora (2008) raises the question whether theReynolds-averaged Navier–Stokes (RANS) equations, based ontemporal averaging, should be the default starting place for allproblems, or whether those based on spatial averaging mightnot be more appropriate. Indeed, one might question why onestarts with a numerical approach at all, involving a discretizationprocess and advanced numerical techniques, when it might beworth the effort to obtain an analytical solution to the governingequation, or a simplified form of them.

Third, a particular difficulty arises in models discretizedinto cells or panels (for depth-averaged models), where severalparameters are used to simulate certain physical flow mecha-nisms in each cell/panel. This raises the issue of equifinality(Aronica et al. 1998). There is usually a lack of sufficiently com-prehensive data from which to select such parameters and henceto calibrate the model without ambiguity for practical use. Forexample, in the Shiono and Knight Model (Shiono and Knight1991, Knight et al. 2010a,b), the choice of the three calibrationparameters (f , l and �) for each panel is fraught with difficul-ties due to lack of measured turbulence data for flows in evengeneric-shaped prismatic channels. Until such work is under-taken, this will inevitably limit the application of this type ofmodel. Recent work by Sharifi et al. (2009, 2010) on the appli-cation of evolutionary computation to open-channel modelling,and by Chlebek and Knight (2006), indicate that it is possible toinvestigate numerically the physical parameters more thoroughlythan hitherto.

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Question 2 – What are the appropriate calibration parametersfor use in 2D and 3D models?

Key issue: model calibration

• 2D and 3D models can provide much improved flow andlevel predictions in many cases, for example on floodplainflows. However, there are issues in model calibration that needresolving.

The use of 2D and 3D models poses particular difficulties withrespect to calibration. Not only does the level of turbulence clo-sure and the values for many turbulence coefficients have to bespecified, but also the time and effort spent on data handlingincreases proportionately. Furthermore, there will often be a lackof any appropriate field data for suitable verification, for example,Reynolds stresses, turbulent intensities, secondary flows, vortexbehaviour, time averaged values of fluxes for use in the RANSequations, etc. Although it is commonly thought that by increas-ing the dimensionality of the model the answers might be more“accurate”, this is not necessarily so, since in 2D and 3D models,there are many more factors that need to be considered. Manyfundamental hydraulic parameters are at present unknown, orin the natural river not easily measurable in sufficient tempo-ral and spatial detail, to make the application of a 3D modelsensible.

This means that approximations are often made in order toproduce simpler models with specific objectives, for example,flood routing, and for predicting stage–discharge relationships,sediment or pollutant transport rates. Any such approximationshighlight the need to understand the assumptions implicit in agiven model and to know the limits of its application. This isillustrated later in Section 5 by reference to a simple lateral dis-tribution model, for steady flows in prismatic channels, aimedat predicting the lateral distributions of depth-averaged veloc-ity and boundary shear stress. However, it is worth re-iteratingthat when dealing with many practical river issues, steady flowsvery often do still need to be analysed (e.g. when estimating con-veyance capacity or in extending stage–discharge relationships),that river reaches or channels are often treated as being prismatic(e.g. reaches near weirs or gauging stations and canals), and thatknowing the distributions of depth-averaged or velocity bound-ary shear stresses across a channel are useful in vegetation andsediment studies.

Question 3 – What is the role of computer software in learningabout river engineering?

Key issue: acquiring knowledge of fluid flow phenomena

• Useful in understanding certain issues, either through numer-ical experiments or through applying a dedicated model to acase study. Both require a model for repetitive calculationsin order to investigate physical effects, boundary changes orcalibration techniques.

• Helpful in understanding fluid flow concepts through flowvisualization of velocity or turbulence data, showing videosof laboratory or natural phenomena, and transmitting teachingnotes with embedded pictures, graphs and comments, maybeon some rare and unusual events.

Many textbooks on fluid mechanics, computing and thermody-namics now come with a CD at the back containing numeri-cal programmes for analysing certain problems, together withteaching materials for learning about advanced techniques innumerical analysis, data processing and modelling. These ready-to-use materials, as well as what can be downloaded directlyfrom the web, are possibly akin to what one buys from thefast-food counter of a supermarket – handy, processed and con-venient, but not to be regarded as the only source of nutrition.One needs a balanced diet, with opportunities to work throughsimple problems by oneself step-by-step, for example, stabilityof numerical procedures as in Abbot and Basco (1989), statisticalquirks, simulation of stage–discharge curves, plotting of isovels,etc.

One pioneering teaching material, developed by Ligget andCaughey (1998), is called “Fluid Mechanics: an interactive text”,which enables the student to learn not only about the basics ofturbulence, stream functions and open-channel flow, but alsoto undertake examples with its embedded Matlab routines. Theearly years of the Flood Risk Management Research Consortium(FRMRC) also developed teaching materials for undergraduateuse, based on commercial software and practical examples. Thesemay be found at www.floodrisk.org.uk and http://frmc.hw.ac.uk.Likewise, the recent conveyance estimation system (CES) maybe used to investigate roughness issues and uncertainty in pre-dicting stage–discharge relationships. The CES features in theConveyance and Afflux Estimation System software, which isfreely available at www.river-conveyance.net. The trend in theuse of computer-based models will increase and already mostcommercial codes produce cut-down versions that are suitablefor student tuition. The cost implications are no doubt a factor,but introducing students to a well-respected brand name makeslong-term commercial sense. Is there a role here for the IAHR todevelop instructional tools, in a similar way to it making a libraryof pictures of hydraulic phenomena available to students?

However, learning from a computer screen is only one wayof acquiring knowledge, as theoretical knowledge learnt in thelecture room or from a book needs the learning experience ofthe laboratory as well. I always try and ensure that PhD stu-dents who mainly pursue numerical studies spend some timewith another student whose work is mainly laboratory-based(and vice-versa), so that they all avoid the dichotomy illustratedin Fig. 1. Although this is more difficult to maintain today, asspecialization increases, it is worth attempting. It is thereforeexpedient to move on from what some call “virtual hydraulics”to take a view of “actual hydraulics”, as maybe acquired in thelaboratory or from fieldwork.

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5 A view from the laboratory

Undergraduate students at Birmingham undertake severalhydraulic experiments in their first semester, one of whichinvolves using Ahlborn visualization tanks with rigid and mobilebeds. They are provided with various objects and thin flexibleplates, together with powder and paint, and asked to see whatthey can learn about fluid flow behaviour involving flow sep-aration, vortex shedding, horseshoe vortices, boundary layers,contraction effects, breaching dynamics, dam failures, etc. Sinceby this stage they have had virtually no formal tuition in fluidmechanics, this can be an advantage, as they can make up theirown minds and try and understand what they see with their owneyes. Someone is always on hand with short “guidance notes”on what they might do, as well as to stimulate questions, offerhelp when required, and interact as a tutor. The aim is to getthem to observe closely, attempt to draw what they see, and sub-sequently produce a report with sketches and seminal concepts,based on their own ideas. This particular experiment is alwayspopular, but incidentally teaches them how difficult it is to cap-ture a particular fluid flow phenomenon in a drawing or sketch,especially in the manner of Leonardo de Vinci. You can oftentell from illustrations of fluid phenomena in textbooks, whetherthe author has actually drawn it from experience or simply useda copy artist.

At the postgraduate level, many papers in research journalshighlight the importance of well-focused experimental studies toelucidate key hydraulic phenomena that are not readily amenableto investigation by purely analytical or numerical models on theirown. The availability of experimental facilities, as well as thestaff who work in the laboratories should never be taken forgranted. Indeed many laboratories in our universities, as wellas at national level, are under threat today due to the high costsinvolved in running them. This is a particularly worrying trend,as now is just the time when, with advanced turbulence modellingbeing used to an ever increasing extent, there is an even greaterneed than ever before to undertake well focused and imaginative

experiments to provide data with which to improve or validatesuch models. This regrettable trend in shunning basic experimen-tal work is highlighted by Nakato and Ettema (1996) on pages450–459. Having studied for my PhD at Aberdeen University,under Professor Jack Allen, who pioneered the use of scale mod-els in the UK (Allen 1947), I have always enjoyed experimentalwork, for which I am grateful, as it has stayed with me throughoutall subsequent numerical and analytical research work.

In my research career involving studies in estuary dynamics,sediment mechanics, boundary shear stresses, overbank flow andfloods, I have selected just one topic to illustrate what mightbe gained by a view from the laboratory. This topic all beganwith a diagram in Chow (1959), in which the distribution ofboundary shear stress in a prismatic channel was given. At thetime I was involved in resistance and sediment studies, involvingthe well-known shear velocity u∗ = (τo/ρ)1/2 that featured inmany equations. When I asked others about the whereabouts ofthe data for τo in such a diagram, I received mainly blank looksfollowed by a long silence. So I began searching for the evidence,and finding only a limited amount, decided to start investigatingit myself. It is always wise to inspect data oneself, and not torely on second-hand knowledge or what people say. I will nowconsider a small part of this topic, how the lateral distribution ofboundary shear stress varies in open-channel flow.

A typical distribution is shown in Fig. 2, for inbank flow ina trapezoidal channel, one of the simplest shapes used in riverengineering. It is but one set, taken from hundreds of experimentsin prismatic channels and closed ducts of various shapes, aimedat trying to understand this phenomenon. This topic proved to bevery useful in acquiring appropriate skills in new experimentaltechniques and error control as well as improving my educationand understanding of secondary flows, planform vorticity, andthe fundamentals of boundary layers, all of which were useful inother research topics.

Figure 2 shows some isovels and four dominant secondaryflow cells for a particular aspect ratio, B/H , together with mea-sured boundary shear stresses on the channel walls and bed.

Figure 2 Flow parameters measured in a trapezoidal channel (after Knight et al. 2010a)

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Figure 3 Boundary shear stresses measured for inbank subcritical flows in a trapezoidal channel for aspect ratios between 1 and 10 and F ≈ 0.48–0.59(after Knight et al. 1994)

Figure 4 Measured boundary shear stresses for inbank supercritical flows in a trapezoidal channel for aspect ratios between 1.5 and 5.3 and F ≈ 3.2(after Knight et al. 1994)

Figure 3 shows part of one set of experiments in which the Froudenumber, F, was held between 0.48 and 0.59 and the aspect ratiovaried from 1.0 to 10.0. The distributions differ with B/H , anddepend on the number and positions of the secondary flow cells.The wider the channel, the more uniform is the distribution ofboundary shear stress in the central region, as would be expected.Figure 4 shows a corresponding set, this time for supercriticalflows with F = 3.2 and aspect ratios between 1.5 and 5.3. Thesignificant influence of secondary flows and aspect ratio on thedistributions may again be seen.

Figure 5 illustrates the integrated values of wall shear stresses,expressed in terms of a percentage of the total shear stress carriedby the channel, plotted against the ratio of wetted perimeters forthe bed and walls, Pb/Pw, rather than in terms of aspect ratio,B/H . This then combines data from rectangular and trapezoidalchannels with differing side slopes. The plot contains a mixture

of open channel and duct data, as well as data from smooth anduniformly roughened channels. There are differences betweenopen channel and closed ducts, too small to see in this figure, butnoticeable in a more detailed analysis of free surface effects. Forfurther details, see Knight et al. (1992, 1994) and Rodi (1980).

Figure 6 shows how an empirically fitted equation to Fig. 5can be used to predict the mean bed shear stress in trapezoidalchannels, with varying side slopes, for both subcritical and super-critical flows. Experiments show that %SFw reduces slightly withF, and this may need to be taken into account when dealing withvery high speed flows, such as occur in some flood-water releasetunnels at high dams where velocities may exceed 60 ms−1. Cav-itation effects then need to be considered. Data from channels inwhich either the walls or bed are roughened differentially fromeach other are given by Knight et al. (1992). Such an empiricallyderived %SFw v Pb/Pw equation can also be used to examine

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Figure 5 Measured percentage boundary wall shear force for inbank flows in a trapezoidal channel for wetted perimeter ratios between 0 and 50(after Knight et al. 1994)

Figure 6 Measured mean bed boundary shear stresses for flows in trapezoidal channels with different side slopes (after Knight et al. 1994)

standard sidewall correction procedures, as shown by Chlebekand Knight (2006). These figures serve to illustrate how a pieceof basic research in one topic aids another topic, such as sedimenttransport, in which flume studies involving composite roughnessfeature strongly. Figure 1 in Section 2 has already drawn attentionto the inter-related nature of topics in river engineering.

Figures 2–6 might appear to reinforce the widely held opin-ion that the “view from the laboratory” is at “too small a scale”and is based on flows in “too idealized conditions”, that is, beingconducted in straight flumes with only simple shapes for cross-sections. Figure 7 is, therefore, inserted as a reminder that naturalriver channels are usually neither prismatic, nor composed of bed

with a uniform roughness distribution over the wetted perimeter,even for inbank flows. The interpretation of laboratory data, andthe application to natural rivers of any subsequently derivedequations, is however problematic.

The same is true for overbank flows, where the flow con-cepts are more complex than for inbank flows, as indicated inFig. 8. Typically, there is a strong lateral shear between thefaster moving flow in the deeper main channel and the slowerflow in the shallower floodplain region. The shear layer produceslarge-scale planform vortices at the floodplain edge, shown bya series of vortices at the interface between the floodplain andmain channel, rotating around vertical axes. These should be

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Figure 7 Concepts to be considered for inbank flows in natural channels (after Knight and Shiono 1996)

Figure 8 Concepts to be considered for overbank flows in prismatic compound channels (after Shiono and Knight 1991)

distinguished from the streamwise vortices, drawn within themain channel, which are driven by the differential gradients inturbulence intensities and rotate around horizontal axes. Bothtypes of vortex are generally present in many flows, but in over-bank flow, one form may dominate another depending on thevalue of the ratio of floodplain depth to main channel depth,Dr. For Dr < 0.3, the planform vortices are large flow structures

with low frequency, extending over the entire width of the flood-plain, even in natural rivers. For higher relative depths, that is,Dr > 0.4, the streamwise vorticity at any re-entrant corner tendsto dominate the flow at the floodplain/main channel interface,making the planform vortices much smaller, as drawn in Fig. 8.One should not, therefore, take this sketch at face value as beingrepresentative of all types of floodplain flow, as some authors do

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when copying this diagram. The planform vortices are drawn rel-atively small here to indicate higher depth flows. This highlightsthe point made earlier about “solidifying” false concepts throughsketches. Alternative sketches of this 3D phenomenon are givenby a number of other authors, such as Fukuoka and Fujita (1989)and van Prooijen et al. (2005). A fuller explanation of the interac-tion between the vortices, with photographs is given by Knightand Shiono (1996), Knight (2008), Chapter 17 of Knight andShamseldin (2006) and in Chapter 2 of Ikeda and McEwan(2009).

Mention should also be made at this point about full-scaleobservations and measurement of flow structures in the field.My own personal view of hydraulics and fluid mechanics hasbenefitted from observing and measuring various mixing, resis-tance, sediment and turbulence phenomena in various estuariesand rivers. Finally, one question that is still asked with surprisingregularity, usually by senior finance officers worried about thecost of maintaining experimental facilities, is the following:

Question 4 – Why are laboratory experiments still needed whencomputers can do it all?

Key issue: without laboratory-based research, we cannotvalidate models effectively

• Laboratory studies sometimes provide the only way of gaininginsights into the behaviour of complex flow patterns undercontrolled conditions, thereby enabling theoretical concepts tobe validated and numerical models to be developed securely.

• Laboratory research often provides the primary data on manyempirical coefficients used in turbulence models, withoutwhich no closure is possible.

Figures 2, 7 and 8 have shown that flow in relatively simpleshapes of prismatic channels is more complex than many peopleimagine. Modelling such flows is not easy and far less straight-forward than modelling stresses in solid mechanics. Indeed,turbulence has often been described as “the outstanding difficultyof our time”. We simply do not know enough about it, or reallywhat turbulence is, given the many types of flow structure thatare implicit in many flow problems (Lighthill 1970). For exam-ple, the relationships between turbulent intensities, Reynoldsstresses, secondary currents, flow structures and boundary shearstress have not been comprehensively measured yet, even forflows in simple channels, such as the trapezoidal one shown inFig. 2.

If such data were available for uniformly roughened channels,over a wide range of aspect ratios, these would provide a soundbasis for many design scenarios and research studies. Furthermeasurements in non-uniformly roughened prismatic channels,and after that in channels of other shapes, would enable modelsto be benchmarked properly against agreed data sets for cer-tain commonly used generic shapes. Ultimately, even more datashould be obtained for non-prismatic channels, involving variousplanform geometries, with the effects of sediments and vegetation

added in as well. Clearly, such a data acquisition programmewould be an enormous undertaking, but until it is done, no tur-bulence model of river flow can be said to be properly validated.This is but one example of where laboratory-based research isneeded, where controlled conditions are possible and measuringfacilities available.

These data would then become the basic building blocks forfuture engineers to benefit from, without having to rely on partialdata sets from individual experiments, written up in numerouspapers, often conducted with differing objectives, and not neces-sarily aimed at this fundamental task. It is what might be regardedas an essential preliminary 3D programme of work, similar to thatundertaken so painstakingly to understand 2D wall-governed tur-bulence and boundary layers. Consider what effort has gone intoinvestigating hairpin vortices, through to the viscous sub-layer,buffer and logarithmic layers to the wake zone, all carried outunder varying pressure gradients, to be followed up by the theo-retical development of displacement thicknesses, thin shear layerequations, and so on. We now benefit from previous decades ofsuch work. Similar work is now needed for 3D flows in openchannels.

6 A view from under the surface

The “views” given in the preceding sections, taken from dif-ferent vantage points, now need to be consolidated by askingsome further questions concerning practical river engineeringissues. To illustrate this, I select another topic that interests me,namely floods. Flood disasters account for about a third of allnatural disasters (i.e. floods, earthquakes or storms) world-wide,but are responsible for over half the deaths. For an introduc-tion and insight into recent flood-related research and somecase studies, see Berz (2000), Knight et al. (2006), Knightand Samuels (2007), Miller (1997) and the FRMRC website(www.floodrisk.org.uk and http://frmrc.hw.ac.uk).

Question 5 – What is wrong with our estimates of flow and level,and what will make them better?

Key issues: extreme flows, composite roughness andhydraulic resistance

• There is high uncertainty in flood levels for extreme flowspredicted by models. One reason for this is that models usesimple roughness parameters, often only calibrated for lowerflows.

• There is uncertainty in deriving “design” flood flows inhydrology for a given return period or frequency, becauseof poor understanding and extrapolation of stage–dischargerelationships.

• Care should be taken to distinguish between roughness andhydraulic resistance.

Discharges and water levels are the primary parameters ofinterest in flood forecasting, flood risk management, floodplain

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modelling, river rehabilitation and geomorphological studies. Atpresent, there is considerable uncertainty about our estimates ofhigh flows, whether it is based on our present gauging methodsand technology, or based on our predictions from mathematicalmodels of the hydrodynamic processes. The fundamental linkbetween discharge and water level is important, since flood riskmaps should give an accurate estimate of water levels and inun-dation areas as possible, as these are used in econometric modelsto quantify flood damage costs, in planning emergency responsestrategies and in flood alleviation design studies. Determining thestage–discharge relationship for channels with complex cross-sections, non-uniform roughness distribution and in unsteadyflow conditions is technically challenging and not a simple mat-ter, as indicated by Ramsbottom and Whitlow (2004), Knight andShamseldin (2006) and Knight et al. (2010b). The CES websitewww.river-conveyance.net also contains many helpful details.

Hydraulic resistance coefficients need to take into account theinteraction between turbulence generated by surface roughness,local topographical features and large-scale flow structures. Val-ues of the coefficients for the local surface roughness should notbe arbitrarily increased to account for these other effects. In prac-tice, this may mean distinguishing between friction, energy andwater surface slopes in 1D river models and taking care in 2Dand 3D models over the use and spatial distribution of “sink”terms and interfacial stresses between cells or panels. Equationsdealing with “patchy” roughness, composite and non-uniformlydistributed roughness should also be examined carefully beforeincorporation into models, as well as those dealing with vege-tation or sediment bed forms. Boundary zones between areas ofdifferent roughness may create particular boundary-related sec-ondary flows, as shown by Ikeda (1981) and Tominaga and Nezu(1991).

For reliable predictions of stage–discharge relationships, themodeller needs adequate turbulence data such as Reynoldsstresses (in order to obtain boundary shear stresses in particu-lar zones) and knowledge of large-scale flow structures (eddies,shear layers and mixing zones). The common practice of relianceon a piece-wise rating relationship, as recommended in the Inter-national Standard ISO 1100-2 (2010), is not suitable for modernhydraulic analyses, where the whole HvQ relationship should beunderstood in terms of the flow behaviour, and related to topog-raphy, fluid mechanisms, resistance and driving forces. It is onlythen possible to extend the HvQ relationship rationally, and in amanner that is easily transferable to other modellers, or hydro-metric staff, building up progressively a more comprehensiveunderstanding as more data become available. In river work, weshould be aiming at measuring what is needed, particularly thatwhich is required for numerical models, and not what is easy ortraditionally undertaken, often just velocities and water level. Isuggest that there should be a flood plain handbook, along simi-lar lines to the flood estimation handbook in the UK, in which allrelevant hydraulic information is kept on HvQ data, roughnessand turbulence data, as well as modelling equations for futurepractitioners to use.

Question 6 – What is the role of broad-scale modelling incatchment flood risk mapping?

Key issue: hydrodynamic modelling is only one aspect ofcatchment modelling

• There is an important role for broad-scale models, makingthe best use of available technology, but recognizing theuncertainties associated with their application.

• There is a need to integrate broad-scale models of differentprocesses, hydraulic, hydrological, flood risk, socio-economicand biological, into a systems approach.

River basin management considers flooding from the governingmeteorological conditions and the point of impact of rainfall onthe land to the discharge of the flood to the sea. It recognizes,evaluates and takes into account the human dimension as well asthe technical and economic cases for intervention, and the envi-ronmental impact of these. River basin modelling is, therefore,not just about hydraulics or hydrology, but also involves social,economic and environmental considerations as well, as shown bythe examples in the FRMRC programme (http://frmrc.hw.ac.ukand www.floodrisk.org.uk) and in several books on catchmentmodelling (Knight and Shamseldin 2006). When viewed from acatchment perspective, or indeed from a national flood risk map-ping perspective, there is a clear need for models that are capableof producing results over a wide area, so-called “Broad-Scale”models. This need is further driven by directives from the Euro-pean Community, such as the water framework directive (WFD)in 2000 and the flood hazard directive in 2006.

Risk is generally accepted to be the product of probability byconsequence, and therefore both should be considered in mod-els. In hydraulic terms, modelling discharge, local velocity anddepth is routine, but with the concept of “flood risk for people”,what is required are combinations of depth and velocity to beevaluated concurrently. Recent work by Shu et al. (2011) andXia et al. (2011), on determining the degree of hazard associatedwith particular depths and velocities in the devastating floods atBoscastle in the UK in 2004, has shown that the application ofdepth–critical velocity relationships for the stability of adults,children and partially submerged cars is useful in highlightingdanger zones. Comparison of the predicted danger zones from theresults of numerical models with video recordings of the actualmovement of cars during the flood were favourable, indicatingthe effectiveness of such tools in planning and siting of car parks,as well as in undertaking risk assessments for people.

The Source–Pathway–Receptor (SPR) modelling of floodimpacts and outcomes is frequently used to assess how the impactof local-scale changes in the runoff generation anywhere in thecatchment (the Source) propagate through the river network (thePathway) to affect flooding downstream (the Receptor). SPRimpact decomposition mapping is the inverse problem in whichone asks the question “How can downstream impacts of a flood(Receptor) be tracked back through the channel network (Path-way) to the local Source areas that created the impact?” This is

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but one example of where inverse questions could usefully beasked of most hydraulic models in order to apply them moreeffectively.

Question 7 – It looks good, but is it correct?

Key issue: accuracy and reliability

• Outputs from numerical models often look impressive but theuser must be able to assess whether they are correct, preferablyby some independent means.

• The performance of hydraulic models is very dependent onthe quality and quantity of calibration data, and so there is aneed to maximize the use of existing data and to understandwhat additional data should be acquired.

How does one check the answers given by a numerical procedureor software package provided by another person or institu-tion? As commercial software becomes easier to use with betteruser interfaces and “hidden” default strategies, questions ariseabout the technical value of such results and output. There isclearly an increasing need for independent checks to be made ofmodel results. The more complex the model, the more difficult itbecomes to comprehend the internal software algorithms used,the default values for coefficients and in some circumstances eventhe flow conditions to be modelled. Despite 3D colour graphicsand virtual reality video images, there is a need to substantiatesuch output, both by the non-specialist user and by the technicalexpert. This is achieved traditionally by benchmarking the soft-ware results against field or laboratory data, against specific testcases for which there are analytical solutions, and in some cir-cumstances by the use of alternative methods. Forensic analysisof model results may become a growth industry by “experts” ina court of law, but it is not for the faint-hearted.

Question 8 – Would an intelligent client save money by improv-ing the job specification?

Key issue: understanding uncertainty and risk

• Clients should be aware of the risks and uncertainties associ-ated with different methods of hydraulic analysis in order tobetter assess and guide decisions.

• Many client representatives have limited knowledge ofhydraulics and rely on the judgement of experts or theirconsultants.

Following on from Questions 4–7, there is a need for any clientto appreciate what is involved in flood risk management mod-elling. For example, the specification for projects used by theEnvironment Agency (EA) in the UK are continually updated toreflect changes in project objectives, experience in the technicalaspects (including feedback from consultants) and the improve-ments in techniques and in the data these techniques use. Forthese improvements to be maximized, the EA, or for that matterany client agency, need to ensure that its own internal hydraulic

knowledge and its skill base are up to date. Large organiza-tions, such as the EA, should not “outsource” all its modellingwork, as this usually leads to a loss of scientific and engineeringexpertise and hence an ability to effectively engage with externalconsultants. Over a number of projects, investment in better spec-ification, more intelligent modelling, and transparent technicallogic, should save money and improve credibility.

Furthermore, the public is now much better informed aboutflood-related topics, and have access to data hitherto not previ-ously available. Flood damage and insurance costs are now moreof a “political” issue than they used to be, and river restorationprojects have likewise heightened the public’s awareness of therole of the river engineer. The public now demand of governingbodies a better quality of “service”, and so the modeller now hasto act together with the public and governing bodies, in partner-ship, to solve local problems. In a litigious society, where conflictarises, the use of litigation may force all technical experts toreview their capability in this area.

The role of the hydraulician in society also needs to change.Elder (1986) stated that “Our most urgent professional need isto become involved with the issues of the day, not as anotherpressure group but as a recognised source of factual information,upon which the public can rely.” Whatever we may think of thisstatement, it should perhaps be debated by IAHR as part of itssocietal responsibility.

Question 9 – What is eco-hydraulics, and why is it important?

Key issue: the natural environment

• There is a growing need to link hydraulics with ecosystems toensure that hydraulically acceptable solutions are acceptablefrom an environmental viewpoint.

• The requirements of the WFD and similar legislation demandour attention.

There is a need to appreciate that the hydraulic behaviour of riversis the key to ecological modelling. The depth of flow, velocityfield, turbulence levels, substrate and vegetation within the riverreach are all governed by the hydraulics. Indeed one might saythat the biology and chemistry are driven primarily by the physicsof the flow. The sciences of hydrology (catchment-scale), geo-morphology, hydrodynamics and eco-hydraulics (catchment andreach-scale) describe the complex interaction between the flowcharacteristics within a channel, the sediment fluxes and the habi-tats. The flow characteristics determine the nutrients, oxygenlevels, movement of sediment, the physical form of the channelbed and vegetation, all of which determine the nature of habitats.

Under the new EC WFD, there is a requirement to achievegood ecological status for all water bodies by 2016, with theexception of heavily modified water bodies. Hydraulicians musttherefore broaden their outlook and to appreciate not only eco-hydrology (Zalewski 2011) and mixing zone regulations foreffluent discharge (Bleninger and Jirka 2011), but also how mod-elling and monitoring towards “ecological good” status should be

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undertaken (Hartnett et al. 2011). These skills should be added tothose traditionally attributed to them, such as understanding thebasis of fluvial processes (Chang 1988), sediment transport andthe principles behind regime theories (White et al. 1982, Bett-ess and White 1987), vegetation biotypes and resistance (Chengand Nguyen 2011) and finally to the possible impact of climatechange on all of these in the future (Bronstert 2006).

7 A view looking downstream

There is one final question that people regularly expect any authorof a “vision” paper to tackle, and that is:

Question 10 – What will be the problems and novel applicationsin 10 or 100 years’ time?

Key issue: knowing the boundary between the unknown andthe unknowable

• Present research must fulfil the requirements of future prac-titioners. Likely, future needs must be kept under constantreview and R and D programmes developed to match thoseneeds.

• It is not always sensible to try and second guess the future.

The scientific basis of hydraulics and fluid mechanics is currentlylargely based on the RANS equations, and that is not likely tochange for some time, despite the RANS approach averaging outlarge-scale motions that can be important (e.g. planform vorticesin overbank flow flood studies). The use of large eddy simula-tion models in river engineering is likely to grow in the future,albeit slowly. Direct numerical simulation models are probablynever likely to be used in practice for decades, if ever. Non-deterministic models and new probabilistic models, based onentropy or other principles, are likely to be developed for specificprocesses.

There is no doubt that new problems and issues will be tack-led in the future. For example, inverse problems are now capableof being solved (e.g. given a velocity field, deduce the turbu-lence coefficients that produce such a flow field). The use ofmodels in this way, both in calibration and application, willlead to new developments in fuzzy logic, uncertainty analysisand in understanding of hydraulic processes. As in hydrology,such questions will be pursued in hydraulics through a range ofconceptual, deterministic and probabilistic models, all demand-ing greater knowledge of basic hydraulics and the underlyingphysics. Benchmarking exercises should increase, as shouldcollaborative work on fundamental processes in jointly ownedlarge-scale experimental facilities, professional networking andsharing of data. This must be good news for our profession aswell as conference organizers.

Having eschewed making any firm predictions about futuredevelopments let me conclude by instead making just threesuggestions:

(1) Share results – the acquisition of both knowledge anddata are costly enterprises. Since rivers are universallypresent in all countries, and no two river basins are iden-tical, we can learn so much more by sharing data andinformation, as well as playing a full part in IAHR con-ferences and technical meetings. The book on New Zealandrivers by Hicks and Mason (1998) is a good example ofhow to share data easily, as are the media used by theFRMRC (www.floodrisk.org.uk and http://frmrc.hw.ac.uk),the UK Flood Channel Facility experimental results (Shionoand Knight 1991; www.flowdata.bham.ac.uk), the CES(www.river-conveyance.net and many more, as evidencedin a selection of websites given before the references.

(2) Shun popularity – at the risk of offending all my aca-demic colleagues, avoid the pernicious influence of “impactfactors” and try instead to:• Measure more and model less;• Think more and publish less.

(3) Relax more – and you let your brain do it for you. Followingthe discovery of a new fundamental particle, consistent withthe Higgs boson, Professor Peter Higgs from the Universityof Edinburgh is reported that he “hit on the concept of theHiggs mechanism in 1964 while walking in the Cairngorms”(The Times Newspaper, 7 July 2012). This just reinforces thesecond quotation by Kennedy given in Section 1. You do notnecessarily need money to set the ball rolling in hydraulicengineering. Building large-scale experimental facilities canwait until later, like the Large Hadron Collider.

I hope you have been stimulated by reading a different styleof paper on river engineering, written from various viewpointsand with perhaps an unusual selection of questions and answers.Enjoy discovering and learning from your own “meanderingpathway” through the science of one of the most delightfulphenomena in the world – our rivers.

Websiteshttp://frmrc.hw.ac.ukwww.floodrisk.org.ukwww.river-conveyance.netwww.flowdata.bham.ac.ukwww.floodsite.netwww.actif-ec.net/library/review_EU_flood_projects.pdfwww.foresight.gov.ukwww.hrwallingford.co.uk/projects/RIBAMOD/index.htmlwww.hrwallingford.co.uk/Mitch/default.htm

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Abbot, M.B., Havno, K., Lindberg, S. (1991). The fourth gener-ation of numerical modeling in hydraulics. J. Hydraulic Res.29(5), 581–600.

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Allen, J. (1970). The life and work of Osborne Reynolds. InOsborne Reynolds and engineering science today, 1–82, D.M.McDowell, J.D. Jackson, eds. Manchester University Press,England.

Anderson, M.G., Walling, D.E.S., Bates, P.D. (1996). Floodplainprocesses. John Wiley, Chichester.

Aronica, G., Hankin, B., Beven, K. (1998). Uncertainty and equi-finality in calibrating distributed roughness coefficients in aflood propagation model with limited data. Adv. Water Res.22(4), 349–365.

ASCE Task Committee on Turbulence Models in HydraulicComputation (1988). Turbulence modelling of surface waterflow and transport, Parts 1-V. J. Hydraulic Eng. 114(9),970–1073.

Ashworth, P.J., Bennett, S.J., Best, J.L., McLelland, S.J. (1996).Coherent flow structures in open channels. John Wiley,Chichester.

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